This invention relates to permanent magnet electrical generator systems and, more particularly, to techniques for connecting and disconnecting permanent magnet generators to electrical systems.
Permanent magnet generators are utilized in a variety of electrical generating systems. Since the field of a permanent magnet generator cannot be de-energized, output voltage is produced when the rotor of the generator is driven by an external power source. Faults, such as short circuits in electrical cables and components external to the generator output terminals, will therefore continue to draw current until the generator stops or the circuit is otherwise disconnected. Mechanical disconnects are used to disconnect a permanent magnet generator rotor shaft from the drive source in certain applications. However, for aircraft applications the weight, expense and design problems presented by high speed operation make mechanical disconnects undesirable. Fuses and circuit breakers can be utilized but they are also undesirable for aircraft applications because they must be manually reset. It is therefore desirable to devise a technique for connecting and disconnecting a permanent magnet generator from an electrical system under both normal operating and fault conditions that can be performed in a relatively light weight system and without manual intervention.